docs: def _get_config(filename):
      """
      Parse the provided YAML file and return a dict.
  
      :parse filename: A string containing the path to YAML file.
      :return: dict
      """
      i = interpolation.Interpolator(interpolation.TemplateWithDefaults,
                                     os.environ)
  
      with open(filename, 'r') as stream:
          try:
              interpolated_config = i.interpolate(stream.read())
              return yaml.safe_load(interpolated_config)
          except yaml.parser.ParserError as e:
              msg = 'Error parsing gilt config: {0}'.format(e)
              raise ParseError(msg)